Japanese Prime Minister Shinzo Abe told Chinese Premier Li Keqiang that rule-based international order must be respected in talks on the sidelines of the Asia-Europe Meeting (ASEM) Friday.
The ASEM summit has been overshadowed by the dispute over China's territorial claims in the South China Sea.
A senior official refused to provide details of their discussions, saying only that Abe had informed Li about "Japan's hitherto known position," Kyodo News reported.
Abe pledged earlier to use the opportunity to urge respect for an international tribunal's rejection of China's claims over nearly all of the South China Sea.
"I'll underscore the importance of the rule of law and peaceful resolution" of the issue, Abe had told reporters late Thursday.
The two neighbouring countries have overlapping claims over islands in the East China Sea, known as Diaoyu to the Chinese and Senkaku to the Japanese.
The Permanent Court of Arbitration in The Hague on Tuesday upheld a complaint brought by the Philippines about contested islets in the South China Sea, which holds key shipping lanes and is believed to be rich in mineral and marine resources.
Analysts say the decisive ruling against China has put Japan in a stronger position in its own territorial dispute with China.
China refused to take part in the arbitration and said the verdict was null and void.
The ASEM summit in the Mongolian capital began earlier Friday with a minute's silence from the 34 heads of government and state from 51 countries in Europe and Asia, for the victims of the previous night's terrorist attack in Nice.
In his opening remarks the host, Mongolian President Tsakhia Elbegdorj, spoke of "very sad news from France."
ASEM leaders jointly issued a statement later Friday, reaffirming their commitment to fight international terrorism and bring to justice those responsible for the attacks "in accordance with the Charter of the United Nations" and other obligations "under international law."
Also Friday, Abe met with European Council President Donald Tusk. The two leaders agreed to conclude a free trade and strategic partnership agreement by the end of this year.
During the meeting, Tusk assured Abe that there will be no shift in the EU's active and open trade and foreign policy amid the uncertainty over Britain's pending withdrawal from the EU.
ASEM was established in 1996 to deepen relations between Asia and Europe.